new research shows.
The findings are “unanticipated ... given concerns for variability between batches of desiccated thyroid cited by national guidelines,” wrote the authors of the study, which was published this month in the Annals of Family Medicine.
In the trial, patients who had been treated for hypothyroidism at Kaiser Permanente Colorado were matched retrospectively into groups of 450 patients each according to whether they were treated with desiccated thyroid or synthetic levothyroxine.
After a follow-up of 3 years, TSH values within normal ranges (0.320-5.500 uIU/mL) were seen at approximately the same rate among those treated with desiccated thyroid and those who received levothyroxine (79.1% vs. 79.3%; P = .905).
“This study showed that after 3 years TSH values in both groups remained within reference ranges approximately 80% of the time,” said Rolake Kuye, PharmD, and colleagues with Kaiser Permanente, in Denver, Colorado.
In an accompanying editorial, Jill Schneiderhan, MD, and Suzanna Zick, ND, MPH, of the University of Michigan, Ann Arbor, say the overall results indicate that the continued use of desiccated thyroid is warranted in some cases.
“Keeping desiccated thyroid medications as an option in our tool kit will allow for improved shared decision-making, while allowing for patient preference, and offer an option for those patients who remain symptomatic on levothyroxine monotherapy,” they advised.
Some variability still seen with desiccated thyroid
Desiccated thyroid (dehydrated porcine thyroid), which was long the standard of care, is still commonly used in the treatment of hypothyroidism, despite having been replaced beginning in the 1970s by synthetic levothyroxine in light of evidence that the former was associated with more variability in thyroid hormone levels.
Desiccated thyroid is still sold legally by prescription in the United States under the names Nature Thyroid, Thyroid USP, and Armour Thyroid and is currently used by up to 30% of patients with hypothyroidism, according to recent estimates.
Consistent with concerns about variability in thyroid hormone levels, the new study did show greater variability in TSH levels with desiccated thyroid when assessed on a visit-to-visit basis.
Dr. Kuye and coauthors therefore recommended that, “[f]or providers targeting a tighter TSH goal in certain patients, the decreased TSH variability with levothyroxine could be clinically meaningful.”
This long-term investigation is “much needed”
This new study adds important new insight to the ongoing debate over hypothyroidism treatment, said Dr. Schneiderhan and Dr. Zick in their editorial.
“[The study authors] begin a much-needed investigation into whether patients prescribed synthetic levothyroxine compared with desiccated thyroid had differences in TSH stability over the course of 3 years.
“Further prospective studies are needed to confirm these results and to explore differences in more diverse patient populations, such as Hashimoto’s thyroiditis, as well as on quality of life and other important patient-reported outcomes such as fatigue and weight gain,” the editorialists added.
“This study does, however, provide helpful information that desiccated thyroid products are a reasonable choice for treating some hypothyroid patients.”